/**
* 抖码算法，让算法学习变的简单有趣
* @作者 : 老汤
*/

// Definition for singly-linked list.
struct ListNode {
    int val;
    ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};

class Solution {
public:
    ListNode* middleNode(ListNode* head) {
        if (head == nullptr || head->next == nullptr) {
            return head;
        }

        ListNode *slow = head;
        ListNode *fast = head;
        while (fast != nullptr && fast->next != nullptr) {
            slow = slow->next;
            fast = fast->next->next;
        }

        return slow;
    }
};